Avoid creating array attributes if possible

Holes in arrays should be represented by an empty
value, not by creating/setting array attributes.

Reason is that the creation is irreversable, and slows
down execution. This speeds up crypto.js by 10%

Change-Id: I2e5472575479a5f2dbe53f59ecb8ed3aeab1be7a
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
inline get_element calls

Inline calls to get_element if the base is an
object with a simple array structure, and the index
is an integer number.

Implemented for 64bit only for now, saves ~25% on crypto.js

Change-Id: I3e34a6409169d90d3937f62264707d52a6c2f9f7
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>